Tardisode 12 acts as a prequel to this episode, recounting the presence of Torchwood from every episode of series 2 where the name had important relevance to the overarching plot threads leading into this story.

Rose Tyler narrates how her life changed when she met the Doctor, who showed her the universe, taking her on a journey she thought would last forever. Then came the army of ghosts, Torchwood, and the war. This is the story of how it all ended, and how she died.

The TARDIS materialises in a playground on the Powell Estate to visit Jackie Tyler. Jackie is overjoyed to see both Rose and the Doctor, but causes Rose concern when she says that she is expecting Rose's grandfather, Grandad Prentice, to come by any minute. Rose explains to the Doctor that her grandfather has been dead for ten years. However, true to Jackie's word, a blurred, ghost-like figure appears in her kitchen at ten past the hour.

Outside, the Doctor and Rose witness more ghosts, walking among ordinary people, who are going about their daily lives calmly despite the manifestations around them. Jackie says that the ghosts will not be around long — the mid-day "ghost shift" only lasts a couple of minutes. At twelve past, somewhere else in London a white-coated technician pulls back a huge lever and the ghosts fade away. A blonde woman, Yvonne Hartman, steps out of her Torchwood Institute office and states that they measured the "ghost energy" at five thousand gigawatts, and congratulates her staff.

A ghost shift.

In Jackie's flat, the Doctor watches various television programmes such as Ghostwatch, EastEnders, and Trisha, which reveal that the ghost phenomenon is international, and that people have accepted it as a regular occurrence. Jackie explains that it started about two months ago. At first, there was panic, but then people realised that they were spirits of their departed loved ones. Jackie says that the ghost she calls her father smells like the cigarettes he used to smoke, but Rose says she smelled nothing. Jackie says that she has to make an effort, and the Doctor notes that the more they want it, the stronger it gets. The ghosts are using peoples' desires and beliefs to press themselves into existence.

At Torchwood Tower, Hartman contacts Dr Rajesh Singh over the Bluetooth earpieces all personnel wear, asking him if he registered any reaction. Singh replies negatively, and reports that their most sophisticated instruments have not been able to read anything off "the Sphere", a large bronze globe floating above him. According to their readings, it simply does not exist. He reaches out to touch it, but an invisible barrier stops his hand.

Two Torchwood workers, Adeola and Gareth, make a clandestine romantic rendezvous. Gareth suggests a secluded location, which is off-limits as it is apparently an area under renovation, but Adeola hesitates. However, when Gareth goes silent, she goes into the section to look for him. As she draws back a curtain, a Cyberman lunges at her and she screams.

The Doctor, singing the Ghostbusters theme, assembles a device to determine the ghosts' origin by triangulation. Rose asks if the ghosts might be related to the Gelth but the Doctor replies negatively; the Gelth were simply coming through the Rift, whereas the ghosts are forcing themselves into existence across the world. He sets up the device in the playground, while Rose monitors the energy levels in the TARDIS. At Torchwood Tower, Hartman cues for the next ghost shift, just as Gareth and Adeola return to their desks, each wearing two Bluetooth earpieces instead of one, the lights on the devices flickering actively.

Jackie, in the TARDIS, comments that Rose has changed a lot. Jackie wonders what will happen to Rose when she is gone and if she will keep travelling, and changing, until she is no longer Rose Tyler, or even human.

The Torchwood machines power up, and the ghosts begin to appear as before. The Doctor traps a ghost within his device, looking at it through 3-D glasses and demanding to know where it comes from. As he adjusts the controls, Torchwood picks up the signal, and Hartman orders the ghost shift closed down. The Doctor has managed to locate the energy source required for the ghosts' appearance but Torchwood has also traced the interference to the Powell Estate. A CCTV camera shows an image of the TARDIS, and Hartman recognises it. The TARDIS dematerialises, with Jackie an unwilling passenger. Hartman, seeing this, realises the Doctor is on his way, and runs off excitedly.

The TARDIS materialises in a Torchwood Tower loading bay, and is surrounded immediately by armed guards. Telling Jackie and Rose to stay inside, the Doctor emerges with his hands raised. Hartman rushes in and to the Doctor's surprise, begins to lead the squad in applause. Hartman greets him warmly, and seems to know a good deal about him, including the fact that he travels with a companion. The Doctor reaches back into the TARDIS and pulls Jackie out, introducing her as "Rose", who unfortunately stared into the heart of the time vortex and aged fifty-seven years (despite Jackie telling the Doctor and Hartman that she is only forty). Rose stays hidden in the TARDIS, watching them through the TARDIS scanner.

Hartman shows the Doctor around the facility.

Hartman welcomes the Doctor to Torchwood, bringing him around and showing him the advanced technology they have captured from alien ships and reverse engineered, all in the name of protecting the British Empire. She explains the Institute's motto: "If it's alien, it's ours," demonstrating it by carting the TARDIS away to a corner of the basement.

Adeola lures another worker, Matt, over to the work area, where she tells him to go towards a mysterious red light. He vanishes behind a plastic curtain and screams as sparks fly and saws whir. He returns to his post later with an extra earpiece. Meanwhile, Hartman reveals that the Doctor was written into the original Torchwood Foundation charter in 1879 as an enemy of the Crown. After his encounter with Queen Victoria and the werewolf, the Queen created the Torchwood Institute to keep Britain great and protect it against the alien horde. The Doctor is their prisoner, but he will be kept comfortable; Hartman hopes that Torchwood will learn a lot from him.

Hartman leads the Doctor to the room with the Sphere, which the Doctor studies with the 3-D glasses before identifying it as a void ship, a hypothetical craft for travelling through the nothingness between parallel universes. That space was called "the Void" by the Time Lords; the Eternals called it the Howling; others call it Hell. When Singh asks how they can get into the Sphere, the Doctor tells them that they should not — they should send it back where it came from.

Hartman explains that the void ship came through to Earth and the ghosts followed in its wake. She shows the Doctor where it came through, at a location opposite her office; when they fire particle engines at the spot, the breach opens. They detected the spatial disturbance as a radar black spot years before, and built Torchwood Tower to reach it, hoping to harness its energy. The public at large know the skyscraper as part of Canary Wharf.

The Doctor demonstrates what the sphere and Torchwood have done.

The Doctor berates Hartman for trying to make the breach bigger, and warns her to cancel the next shift. He explains, using a piece of glass as a demonstration, that when the sphere came through, it cracked the surface of this dimension. The ghosts have been bleeding through the fault lines, walking from their world to this one. However, too many ghosts and (breaking a piece of glass) the surface will shatter. When Hartman insists on going through with the shift anyway, the Doctor abruptly changes gears, casually sitting to watch it happen. Hartman, disconcerted, stops the countdown, conceding that it may be prudent to get more intelligence. However, once they go into Hartman's office, Adeola, Matt and Gareth restart the countdown.

Meanwhile, Rose leaves the TARDIS and, picking up a stray laboratory coat, makes her way to the room with the void ship. There she uses the psychic paper to get through the door. When Singh questions her, she tries to bluff her way with the psychic paper; however, all Torchwood personnel have received basic psychic training and he sees it as blank paper. Singh calls for security and tells his assistant Samuel to check the locks. To Rose's surprise, "Samuel" is Mickey Smith, who signals Rose to keep quiet.

Hartman notices the ghost shift programme powering up, but despite her orders, the three workers continue their work. As the power rises, the void ship activates, shaking the whole room. The Doctor recognises that the workers are being controlled through the earpieces; he apologises, and uses the sonic screwdriver to disrupt the signal. The three cry out and collapse; Jackie accuses the Doctor of having killed them, but he replies that they were already dead. The Doctor removes one of Adeola's earpieces, and, to her disgust, Hartman sees a long string of nerve tissue dangling from it, indicating it was connected straight to her brain. The ghost shift is now at ninety percent.

The Doctor traces the control signal to the work area and he and Hartman rush there, not hearing Singh's communication about the void ship, whose existence is beginning to register on Singh's instruments. The doors to the void ship room seal, locking in Rose, Mickey and Singh. Mickey, more confident than he once was, assures Rose that they have beaten them before and they will beat them again. At the work area, the Doctor, Hartman and two soldiers investigate in the corridor location where the three employees were "turned" and they find themselves surrounded by the advance guard of Cybermen.

Mickey tells Rose that the Cybermen were nearly beaten on the parallel Earth but they somehow escaped, finding a way to this world — despite the Doctor's pronouncements that this travel was impossible.

The Cybermen lead the Doctor and Hartman as prisoners back to the breach, where they kill the technicians trying to shut the programme down. A Cyberman with black handlebars on its helmet (the Cyber-Leader) orders the ghost shift be increased to one hundred percent.

All around the world, the ghosts shimmer into full existence, revealing themselves to be Cybermen. World-wide panic ensues as the Cybermen march across the face of the planet, killing people and breaking into homes. Hartman calls it an invasion, but the Doctor notes it is too late for that — it is a victory. In the void ship room, the sphere begins to open up. Mickey pulls out a large rifle from its hiding space and aims it toward the ship, expecting some sort of Cyber-Leader variant to emerge.

The Void ship opens.

The Doctor asks the Cyber-Leader about the void ship, claiming that the Cybermen do not have the necessary technology to build one. To the Doctor's horror, the Cyber-Leader confirms that the sphere is not theirs and they do not know its origins. It broke down the barrier between worlds, and they merely followed.

As Singh, Rose and Mickey watch in horror, a black Dalek and three gold Daleks emerge from the void ship, along with a mysterious device. The black Dalek approaches the three humans; it announces the location as Earth, that lifeforms have been detected, and gives the order to exterminate, a command echoed by the other Daleks.

Not every person who worked on this adventure was credited. The absence of a credit for a position doesn't necessarily mean the job wasn't required. The information above is based solely on observations of the actual end credits of the episodes as broadcast, and does not relay information from IMDB or other sources.

The Doctor says, "Allons-y" and "Allons-y, Alonso!" for the first time. He would get to say "Allons-y, Alonso" to an actual Alonso in Voyage of the Damned. For those who do not speak French, a translation ("Let's go!") would not be provided until Midnight, two years later.

Freema Agyeman makes a pre-Martha appearance in this episode as the doomed Torchwood worker Adeola Oshodi. Russell T Davies has stated that he would have rewritten this episode so that Adeola survived had he known Agyeman would turn out to be a perfect casting choice to fill the soon-to-be-vacant companion role.

Graeme Harper's penchant for including a distorted image of a main character is present in this story. Though not included in every single story he's directed for BBC Wales, it's seen often enough to be considered something of a directorial "signature". Similar distortion is achieved through the use of other magnifying glasses in The Unicorn and the Wasp and Utopia, a curved window in Journey's End, and with mirrors in Turn Left. This time, it's the Doctor that gets "the Harper treatment".

The scene in which the Doctor asks the Cyber-Leader about the Void Ship is similiar to The Parting of the Ways when the Doctor asked the Dalek Emperor how it came up with the word Bad Wolf, which also had the Dalek Emperor replying that it had nothing to do with him, much like the Cyber-Leader said in this episode.

The characters Gareth Evans and Adeola Oshodi, while presumed to have died at the end of Army of Ghosts, have definite parallels with the future Torchwood couple of Ianto Jones and Lisa Hallett: all four worked for Torchwood London, Gareth had a penchant for suits and bold coloured shirts, both couples were biracial, and they were all caught up in the Cybermen-Dalek attack on Torchwood at Canary Wharf. The character's name Gareth correlated with Ianto Jones's actor Gareth David-Lloyd. Furthermore, flashbacks during Cyberwoman revealed Ianto dragging Lisa through Torchwood London in a room filled with plastic sheeting that was identical to the room and scene where Adeola was converted by the Cybermen after following Gareth into a cordoned off room.

When the name of the episode was revealed it was heavily rumoured that the titular ghosts referred to the Gelth who would return to the show in that episode. These rumours were clearly proven false as the ghosts turned out to be Cybermen coming through from the parallel world whose appearance and physical form was distorted by their movement through the void.

When Rose presents her mother with the Bazoolium, she's holding it in her left hand. When the view switches to look at Jackie, it shifts to Rose's right hand and then immediately back to her left when the view returns to the original vantage point.

When the Cybermen kill the Ghostwatch presenter there is no electricity going through his body.

When Rose is in the bus at the beginning of the episode, a man boards the bus and sits on the seat behind her, but when the camera pull out to another shot, the man is in the second row behind her.

When Yvonne and the Doctor stand outside the doors to the Sphere room, a Torchwood sign is seen behind them. When Rose stands in the same place further on in the episode, the same sign is seen but with extra additions.

The Doctor breaks the glass in Yvonne's office with his sonic screwdriver, but after the Doctor tells Jackie that he has a reputation to maintain, the glass is fixed.

Because of the ubiquity of this race, no attempt will be made here to list every appearance in every medium. Instead, we focus on televised appearances here, and invite you to explore a complete list of appearances elsewhere.